Locked-in syndrome

Locked-in syndrome (LIS) is a rare condition caused by bilateral damage to the ventral pons, most often due to a stroke. LIS is characterized by quadriplegia and bulbar palsy or pseudobulbar palsy, caused by the interruption of the corticospinal and corticobulbar tracts in the pons. The only remaining voluntary muscle movements include vertical eye movement and blinking. Consciousness, awareness, cognition, and sensation are preserved. Diagnosis of pontine damage is made on a CT or MRI of the brain. Preserved cognition is diagnosed via EEG and neuropsychological testing. Management in most patients includes tracheostomy, mechanical ventilation, placement of a feeding tube, and physiotherapy. Patients learn to communicate through blinking and/or eye movements and the help of computer programs/speech synthesizers. Some patients may recover a certain degree of motor control, speech, and swallowing ability.

• Ventral pontine damage/injury
  • Bilateral ventral pontine stroke (most common)
    • Ischemic stroke (thrombotic/embolic occlusion of the basilar artery)
    • Hemorrhagic stroke
  • Direct trauma to the ventral pons
  • Pontine demyelination (e.g., multiple sclerosis affecting the ventral pons, central pontine myelinolysis)
  • Brain tumor or brain abscess affecting the ventral pons
  • Acute disseminated encephalomyelitis (postinfectious or postimmunization)
• Other diseases
  • Amyotrophic lateral sclerosis
  • Guillain-Barré syndrome
  • Myasthenia gravis

To remember that locked-in syndrome is caused by the damage to the ventral (i.e., basilar) part of the pons, think of someone locked in the basement.

References:^[1][2][3][4]

Locked-in syndrome is typically preceded by a loss of consciousness and subsequent coma lasting for days or weeks. The following symptoms are detected on regaining consciousness:

• Paralysis of voluntary muscles
  • Paralysis of all 4 limbs and torso (quadriplegia)
    • Caused by interruption of the bilateral corticospinal tracts as they pass through the ventral pons.
    • Characterized by spasticity, ↑ deep tendon reflexes, positive bilateral Babinski's sign
  • Bulbar palsy or pseudobulbar palsy
    • Anarthria: a severe form of dysarthria characterized by the inability to speak due to impaired neuromuscular control of the muscles used for speech
    • Dysphagia (inability to swallow)
  • Horizontal gaze palsy: caused by damage to the center for horizontal gaze and the VI^thcranial nerve nucleus, which both lie in the pons
  • Respiratory abnormalities
    • Cheyne-Stokes breathing, apnea, loss of voluntary control of breathing
    • Often requires tracheostomy and mechanical ventilation
• Preservation of the following functions
  • Normal consciousness, language comprehension, cognition, and ability to make decisions (the cerebral cortex and reticular activating system are undamaged/preserved)
  • Vertical eye movements and voluntary blinking
  • Cutaneous sensation

Patients with LIS can only communicate by blinking and vertical eye movements!

Patients with locked-in syndrome due to basilar artery occlusion are blocked like a basalt rock!

References:^{[5][6][7][8][9]}

• CT/MRI of the brain: : indicated in all patients to identify the underlying cause
• EEG
  • Indicated in all patients to rule out brain death
  • Used to measure visual/auditory evoked potentials → nearly normal EEG in LIS
• Lumbar puncture: indicated if an infectious etiology or Guillain-Barré syndrome is suspected
• Neuropsychological testing
  • Performed once the patient is stable to assess cognition
  • Patients communicate with eye movements or blinking in response to the test questions → normal or near-normal cognition

Demonstration of preserved cognition, vertical eye movements, and blinking in a quadriplegic, anarthric patient is diagnostic of LIS!

References:^{[4][5][10][11][12][13]}

• Persistent vegetative state (PVS)
• Akinetic mutism

References:^[5][14][15]

The differential diagnoses listed here are not exhaustive.

• In acute phase
  • Supportive therapy (airway, breathing, circulation)
  • Treat the underlying, often life-threatening, disorder (see “Etiology” for causes)
• In the rehabilitative phase
  • Respiration: most patients require tracheostomy and mechanical ventilation
  • Feeding: initially nasogastric or orogastric tube; possibly gastrostomy tube
  • Physiotherapy: passive stretching exercises; skeletal muscle relaxants and/or botulinum toxin for spasticity; frequent position change to avoid pressure sores
  • Speech: eye-gaze sensor-controlled computer communication programs, computer/internet use; use of speech synthesizers; eyelid blinking to communicate yes/no

References:^[15][16]

• Patients with LIS may show
  • Complete recovery (transient LIS): e.g., in patients with Guillain-Barré syndrome
  • Moderate recovery: recovery of some motor function, ability to breathe and/or swallow, independence in some activities of daily living
  • Minimal to no recovery

References:^[7][16]